Radio frequency switch employing reed switches and a quarter wave line

ABSTRACT

An antenna switching relay for selectively switching an antenna to a transmitter or a receiver of a radio transceiver includes a pair of normally open reed switches and a quarter wave transmission line. In the receive mode, the reed switches are open and the antenna is connected to the receiver through the quarter wave transmission line. In the transmit mode, the reed switches are closed and the antenna is connected to the transmitter through one of the reed switches, while the other reed switch shorts out the receiver end of the transmission line, thereby causing an open circuit to be reflected to the antenna terminal thereof.

United States Patent 1191 Kowalewski RADIO FREQUENCY SWITCH EMPLOYING REED SWITCHES AND A QUARTER WAVE LINE [75] Inventor: Rolf E. Kowalewski, Palatine, Ill. [73] Assignee: Motorola, Inc., Franklin Park, Ill. [22] Filed: Sept. 7, I972 [2]] App]. No.: 287,129

[ Mar. 26, 1974 Attorney, Agent, or Firm-Stanley J. Tomsa; Eugene A. Parsons; Vincent J. Rauner [57] ABSTRACT An antenna switching relay for selectively switching an antenna to a transmitter or a receiver of a radio {52 us. 01 .1 325/23, 335/5, 335/152 T a 0f W' 9 mad switches and a quarter wave transm1ss1on lme. In the [51] Int. Cl. I-I0lp 1/10 d th d h d th 58 Field of Search 325/21, 22, 23; 343/178, B F e 343/180; 335/4, 5 152, 127; 200/153 S; tenna1s connecte to t e recelvert roug t e quarter wave transm1ss1on l1ne. In the transm1t mode, the reed 333/7, 13

swltches are closed and the antenna 15 connected to 1561 3::35::"12255121211122223: 12123255211 51 UNITED STATES PATENTS the transmission line, thereby causing an open circuit 3,327,215 6/1967 Battin ct a1. 343/180 X to b r fl t d to the antenna terminal thereof. 3,562,597 2/1971 White v 335/5 X 3,030,468 4/1962 Donceel et a1 335/152 6 Claims, 2 Drawing Figures /2 1 TRANS/Ill 77' E I? RECEIVER BACKGROUND 1. Field of Invention This invention relates generally to radio frequency switches, and more particularly to antenna switches for radio transceivers.

There are many applications wherein it is necessary to provide a switch for radio frequency electrical signals. One such application is in a radio transceiver wherein it is desired to selectively switch an antenna to either the transmitter or receiver thereof.

2. Prior art Several techniques for providing an antenna switching function are known. One such system employs a double-pole single-throw, or form C, relay to connect the antenna to the receiver when the relay is deenergized, and to connect the antenna to the transmitter when the relay is energized. Another such system employs a pair of magnetically operated reed switches, one of which is normally closed for connecting the receiver to the antenna, and another which is normally open for connecting the antenna to the transmitter. A third technique employs diode switches to provide the antenna switching function.

Whereas these techniques provide a way to selectively connect an antenna to either a transmitter or a receiver, aform C relay is generally costly, does not provide good isolation between the transmitter and receiver, and is easily contaminated by dirt and other foreign matter. Reed switches are hermetically sealed to minimize the contamination problem, however only normally open reed switches are readily available for use at high radio frequencies such as the VHF band. Therefore, two switches must be used, and one must be biased closed by means of a permanent magnet or electromagnet. Diode switches are limited in power handling capability and tend to generate undesired intermodulation products and harmonics.

SUMMARY ltis an object of the present invention to provide an improved antenna switching system that provides a good RF connection between connected terminals while maintaining good isolation between disconnected terminals.

It is a further object of this invention to provide an antenna switching system that utilizes readily available normally open reed switches and does not require a form C relay or a normally closed or magnetically biased reed switch.

A still further object of this invention is to provide an antenna switching system that minimizes contact contamination and the generation of undesired frequency components.

In accordance with the preferred embodiment of the invention, a first normally open reedwswitch is connected between an antenna and a radio transmitter. A

one quarter wavelength transmission line is connected In the receive mode, the reed switches are deenergized and the receiver is connected to the antenna through the quarter wave transmission line. Energizing the electromagnet causes the transmitter to be connected to the antenna by means of the first reed switch and causes the second reed switch to short out the input terminals to the receiver. The short circuit at the receiver end of the quarter wave transmission line is reflected as an open circuit to the antenna end thereof,

thereby preventing any mismatch from occurring at the antenna.

DESCRIPTION OF THE DRAWING In the drawing:

FIG. I is a schematic circuit diagram of the radio frequency switching system according to the invention; and

FIG. 2 is a perspective drawing of a practical embodiment of the antenna switching system according to the invention.

DETAILED DESCRIPTION Referring to FIG. 1, there is shown an antenna 10 connected to one terminal of a normally open reed switch 12 and to the center conductor of a one quarter wavelength transmission line 14. Although .a quarter wave transmission line is shown, any impedance inverting network such as a wave guide, lumped circuit element network or transmission line having a length equal to an odd integral number of quarter wavelengths such as one quarter wavelength, three quarters wavelength, etc., may be used. A coaxial connector 16 is used to make the connection between the antenna 10 and the switch 12 and line 14, however, a direct connection may be made without the use of the connector 16. A transmitter 18 is connected to the other terminal of the reed switch 12. The other end of the one quarter wavelength transmission line 14 is connected to a receiver 20 through a second coaxial connector 22. The shield of the transmission line 14 is connected to ground and a second reed switch 24 is connected be tween ground and the ungrounded conductor of the transmission line 14 through a capacitor 26. An activating means, in this embodiment, an electromagnet having a coil portion 30 and pole pieces 32 and 34 is magnetically coupled to the reed switches 12 and 24. The coil 30 is energized by applying an electrical current to a pair of leads 36 and 38 from a suitable power source (not shown) such as, for example, the transmitter power supply.

In operation, when the transceiver is operating in the receive mode, the coil 30 is not energized and the reed switches 12 and 24, which are hermetically sealed reed switches well known in the art, are open. When the switches 12 and 24 are open, the receiver 20 is connected to the antenna 10 through the quarter wave transmission line 14 to allow the receiver 20 to receive signals picked up by the antenna 10. When it is desired to transmit a signal from transmitter 18, the coil 30 is energized from the power source, thereby causing magnetic flux to flow between the pole pieces 32 and 34 through the reed switches 12 and 24 to close the reed switches 12 and 24. Closing the reed switch 12 completes the path between the transmitter 18 and the antenna 10, and allows signals from transmitter 18 to be applied to the antenna 10 for transmission. Simultaneously, the reed switch 24 provides a path between the antenna terminal of the receiver 20 and ground through the capacitor 26, which has a value chosen such that capacitor 26 resonates with the inductance of the reed switch at radio frequencies. The low impedance of the series combination of capacitor 26 and reed switch 24 between the receiver antenna terminals and ground shunts any signals from transmitter 18, which may pass through the transmission line 14, to ground, thereby preventing signals from transmitter 18 from damaging the receiver 20. The termination of the transmission line 14 provided by the series combination of capacitor 26 and reed switch 24, which is a low impedance and may be chosen to be substantially a short circuit, appears as a high impedance at the terminal of transmission line 14 that is connected to the antenna 10. When the impedance provided by the capacitor 26 and reed switch 24 is substantially a short circuit, the impedance that is reflected to the antenna through the quarter wave transmission line 14 is substantially an open circuit, thereby preventing the closed reed switch 24 from substantially affecting the signal flowing from the transmitter 18 to the antenna 10.

In the switching system of the present invention, both of the reed switches 12 and 24 are either open or closed, thereby eliminating biasing magnets which are required in switching systems of the prior art wherein one of the reed switches is open while the other is closed. In addition, when the transceiver is in the receive mode, which is a major portion of the time, the electromagnet coil 30 is not energized, thereby saving electrical power. The electromagnet coil 30 need be energized only during the relatively brief intervals when a transmission from transmitter 18 is taking place. The receiver is isolated from the transmitter 18 during transmission by the low impedance to ground provided by the capacitor 26 and reed switch 24 when the reed switch 24 is closed during transmission.

Referring to FIG. 2, there is shown in perspective view a preferred embodiment of the antenna switching system according to the invention. Like numbers are used to indicate analogous components in FIGS. 1 and 2. The components comprising the antenna switching system are mounted on a board 40 having copper cladding 52 bonded thereto. The reed switches 12 and 24 are mounted directly on the board 40, and the electromagnet assembly comprising the coil 30 and pole pieces 32 and 34 is mounted over the reed switches. The reed switches 12 and 24 are positioned on opposite sides of the coil 30 to minimize electromagnetic coupling between the switches. The pole pieces 32 and 34 are steel pole pieces extending from the coil 30 to simultaneously couple magnetic flux from the coil 30 to the reed switches 12 and 24. The magnet coil 30 is energized by applying electric current to leads 36 and 38 as in FIG. 1. The reed switch 24 is connected to the copper cladding 52 at point 41 to provide the gound connection and to the capacitor 26 through the island 42. The capacitor 26 is coupled to the transmission line 14 through another island 44.

The transmission line 14, in this embodiment, is a strip line or microstrip type of transmission line comprising a ceramic or other dielectric substrate 46, a screened or printed conductor 48, which is analogous to the center conductor of a coaxial transmission line,

on oneside of the ceramic substrate, and a copper,

ground plane 50 on the opposite side of the substrate. The copper ground plane 50 of the transmission line 14 is connected to the copper cladding 52 of the board 40 to provide a ground connection to the ground plane 50. This connection if analogous to the ground connection made to the shield of the transmission line 14 of FIG. 1. The printed conductor 48 has one end connected to the capacitor 26 and the other end connected to the reed switch 12 and the antenna connector 16 (not shown in FIG. 2). The island 44 connects the transmission line 14 to the center conductor of the receiver jack 22. The outer conductor of the jack 22 is connected to the copper cladding 52 to provide a ground. The transmitter 18 (not shown in FIG. 2) is connectible to the island 54 for connection to the reed switch 12. Operation of the circuit of FIG. 2 is similar to the operation of the circuit of FIG. 1, already explained.

The embodiment of the antenna switching system according to the invention shown in FIG. 2 is included as an illustration of a practical embodiment of the system. It should be noted that variations of the basic system, such as, for example, the use of a coaxial rather than a microstrip transmission line for line 14, different placement of the reed switches 12 and 24 and a different configuration of pole pieces 32 and 34 may be used and still fall within the scope of the invention. In addition, although the switching system according to the invention has been illustrated in a system using unbalanced transmission lines (one conductor grounded), the techniques are equally applicable to systems utilizing balanced transmission lines wherein both conductors are floating.

I claim:

1. A radio frequency switch for operation at a predetermined frequency for selectively coupling one of a transmitter and a receiver to a common antenna, including in combination:

a mounting board;

first and second magnetically actuated reed switches mounted on said mounting board, each reed switch comprising a normally open magnetic reed contact pair, each reed switch having a first conductor extend ng'from one of the contacts of said pair and a second conductor extending from the other of the contacts of the pair;

a microstrip transmission line mounted on said board, said microstrip transmission line having a quarter wavelength conductor at said predetermined frequency having first and second ends and a common conductor;

means for connecting the first conductor of said first reed switch and the first end of said quarter wavelength conductor to said antenna;

means for connecting the second conductor of said first reed switch to said transmitter;

means for connecting the second terminal of said quarter wavelength conductor to said receiver and to the first conductor of said second reed switch;

means for connecting the second conductor of said second reed switch to the common conductor of said microstrip transmission line; and

a magnetic actuator mounted to said mounting board, said magnetic actuator having an electromagnetic coil positioned between said reed switches, said actuator having a pair of magnetic pole pieces attached to said electromatic coil and extending radially therefrom beyound the radius of the electromagnetic coil and overlapping said reed switches for simultaneously closing said reed switches when said electromagnetic coil is energized for allowing radio frequency signals to flow between said transmitter and said antenna.

2. A radio frequency switch as recited in claim 1 wherein the transmission line comprises a dielectric substrate having said first conductor bonded thereto.

3. A radio frequency switch as recited in claim 2 wherein said means connecting the first conductor of said second reed switch to the second terminal of said quarter wavelength conductor includes a capacitor.

4. A radio frequency switch as recited in claim 3 wherein the capacity of said capacitor is chosen for resonance with the inductance associated with said second reed switch at the operating frequency of said radio frequency switch.

5. A switch as recited in claim 1 wherein each pole piece has an edge contacting a major surface of said mounting board, and wherein each of said edges has a pair of notches defined therein for receiving said reed switches.

6. For use with a radio frequency antenna switching system employing a quarter wavelength transmission line, an electrically actuated switch, comprising:

a mounting board,

first and second magnetically actuated reed switches sealed normally open magnetic reed contact pair; and

an electromagnetic actuator mounted to said board,

said actuator having a bobbin having first and second opposing ends and a single coil of conductive wire wound around the bobbin, said bobbin being positioned between said reed switches and parallel thereto, said actuator having first and second planar pole pieces attached to the first and second ends of said bobbin, respectively, and extending radially from said bobbin beyond the radius of said coil and partially encircling said reed switches, each of said pole pieces having a substantially straight edge contacting said mounting board, each of said substantially straight edges having first and second notches defined therein for receiving said reed switches, said pole pieces being positioned substantially perpendicular to said mounting board and adaped to conduct magnetic flux from said coil to said reed switches for simultaneously closing both of said magnetic reed contact pairs upon electrical energization of said coil. 

1. A radio frequency switch for operation at a predetermined frequency for selectively coupling one of a transmitter and a receiver to a common antenna, including in combination: a mounting board; first and second magnetically actuated reed switches mounted on said mounting board, each reed switch comprising a normally open magnetic reed contact pair, each reed switch having a first connector extending from one of the contacts of said pair and a second conductor extending from the other of the contacts of the pair; a microstrip transmission line mounted on said board, said microstrip transmission line having a quarter wavelength conductor at said predetermined frequency having first and second ends and a common conductor; means for connecting the first conductor of said first reed switch and the first end of said quarter wavelength conductor to said antenna; means for connecting the second conductor of said first reed switch to said transmitter; means for connecting the second terminal of said quarter wavelength conductor to said receiver and to the first conductor of said second reed switch; means for connecting the second conductor of said second reed switch to the common conductor of said microstrip transmission line; and a magnetic actuator mounted to said mounting board, said magnetic actuator having an electromagnetic coil positioned between said reed switches, said actuator having a pair of magnetic pole pieces attached to said electromatic coil and extending radially therefrom beyound the radius of the electromagnetic coil and overlapping said reed switches for simultaneously closing said reed switches when said electromagnetic coil is energized for allowing radio frequency signals to flow between said transmitter and said antenna.
 2. A radio frequency switch as recited in claim 1 wherein the transmission line comprises a dielectric substrate having said first conductor bonded thereto.
 3. A radio frequency switch as recited in claim 2 wherein said means connecting the first conductor of said second reed switch to the second terminal of said quarter wavelength conductor includes a capacitor.
 4. A radio frequency switch as recited in claim 3 wherein the capacity of said capacitor is chosen for resonance with the inductance associated with said second reed switch at the operating frequency of said radio frequency switch.
 5. A switch as recited in claim 1 wherein each pole piece has an edge contacting a major surface of said mounting board, and wherein each of said edges has a pair of notches defined therein for receiving said reed switches.
 6. For use with a radio frequency antenna switching system employing a quarter wavelength transmission line, an electrically actuated switch, comprising: a mounting board, first and second magnetically actuated reed switches mounted on said mounting board in a parallel spaced relationship, each reed switch having a sealed normally open magnetic reed contact pair; and an electromagnetic actuator mounted to said board, said actuator having a bobbin having first and second opposing ends and a single coil of conductive wire wound around the bobbin, said bobbin being positioned between said reed switches and parallel thereto, said actuator having first and second planar pole pieces attached to the first and second ends of said bobbin, respectively, and extending radially from said bobbiN beyond the radius of said coil and partially encircling said reed switches, each of said pole pieces having a substantially straight edge contacting said mounting board, each of said substantially straight edges having first and second notches defined therein for receiving said reed switches, said pole pieces being positioned substantially perpendicular to said mounting board and adaped to conduct magnetic flux from said coil to said reed switches for simultaneously closing both of said magnetic reed contact pairs upon electrical energization of said coil. 